Many material processing operations are presently performed using machine tools that operate under numerical control (NC). In a typical NC machine installation, a set of programmed instructions is processed by a machine tool unit (MTU) that provides motion control signals to servomechanisms coupled to the machine tool. A work piece retained by the machine tool is thus processed into a finished part according to the programmed instructions. The instructions are typically prepared by machine tool programmers who develop the instructions based upon available geometrical information for the finished part, which generally includes drawings of the part, either in paper or electronic form. The machine tool programmers also typically include process-related instructions, which may include feed rates for the work piece and even the selection of one or more forming tools such as drills, end mills, or other like forming devices that are driven by the NC machine.
In one particular application, the machine tool may be used to control a welding path in a friction stir welding (FSW) device. FSW is a process for joining metals that does not include the use of filler materials. Instead, a weld is developed along a pre-determined path through a combined action of frictional heating and mechanical deformation of the metal. Briefly, the FSW device rotates and impresses a FSW tool against a surface of the work piece that generates the required frictional heating and mechanical deformation. The FSW tool is progressively moved along a pre-determined path in conformity with the programmed instructions provided to the MTU.
The programmed instructions are generally encoded on a variety of transportable memory devices, which may include punched tapes, magnetic tapes or disks, or optical disks. The programmed instructions are then introduced to the MTU from the transportable memory device using a reader configured to read the transportable memory device. Occasionally, errors occur when the instructions are programmed that may result in one or more defects in the finished part. For example, incorrect geometrical information may be encoded in the instructions so that a part is produced having a weld path that departs from a desired weld path. Programming errors may also include process-related information, so that the work piece may, for example, be subjected to an incorrect feed rate during a portion of the welding process. In either instance, the work piece must be subjected to expensive rework procedures to salvage the part. Alternately, if the work piece cannot be salvaged, it must be entirely scrapped.
Accordingly, what is needed is a system and method for verifying a process path in an NC-controlled system that allows errors to be readily identified and corrected.